linux-kernel - Re: [PATCH v1 35/35] drm/modes: Introduce more named modes

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Date:   Thu, 25 Aug 2022 16:22:33 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Noralf Trønnes <noralf@...nnes.org>
Cc:     Jernej Skrabec <jernej.skrabec@...il.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Jerome Brunet <jbrunet@...libre.com>,
        Samuel Holland <samuel@...lland.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Daniel Vetter <daniel@...ll.ch>, Emma Anholt <emma@...olt.net>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Kevin Hilman <khilman@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Phil Elwell <phil@...pberrypi.com>,
        Mateusz Kwiatkowski <kfyatek+publicgit@...il.com>,
        linux-arm-kernel@...ts.infradead.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        linux-amlogic@...ts.infradead.org, dri-devel@...ts.freedesktop.org,
        Dom Cobley <dom@...pberrypi.com>
Subject: Re: [PATCH v1 35/35] drm/modes: Introduce more named modes

On Sun, Aug 21, 2022 at 06:16:15PM +0200, Noralf Trønnes wrote:
> 
> 
> Den 29.07.2022 18.35, skrev Maxime Ripard:
> > Now that we can easily extend the named modes list, let's add a few more
> > analog TV modes that were used in the wild, and some unit tests to make
> > sure it works as intended.
> > 
> > Signed-off-by: Maxime Ripard <maxime@...no.tech>
> > 
> > diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> > index 3634ac9f787d..09ed5ce7746d 100644
> > --- a/drivers/gpu/drm/drm_modes.c
> > +++ b/drivers/gpu/drm/drm_modes.c
> > @@ -1853,7 +1853,9 @@ struct drm_named_mode {
> >  
> >  static const struct drm_named_mode drm_named_modes[] = {
> >  	{ "NTSC", &drm_mode_480i, DRM_MODE_TV_NORM_NTSC_M, },
> > +	{ "NTSC_J", &drm_mode_480i, DRM_MODE_TV_NORM_NTSC_J, },
> >  	{ "PAL", &drm_mode_576i, DRM_MODE_TV_NORM_PAL_B, },
> > +	{ "PAL_M", &drm_mode_480i, DRM_MODE_TV_NORM_PAL_M, },
> 
> Please use a dash instead of an underscore to keep it consistent with
> what's used elsewhere.

Yeah, I tried not to use it since I didn't want to cripple the parser
with bad heuristics, but Geert has done a much better job than my
attempts here:
https://lore.kernel.org/dri-devel/2eb205da88c3cb19ddf04d167ece4e16a330948b.1657788997.git.geert@linux-m68k.org/

I've taken that patch in, renamed the modes and we already have unit
tests in other patches to cover that part of the parser.

> I tried to use PAL and set the connector as connected, but that didn't
> work: video=Composite-1:PALe
> 
> Is this a bug and it should work or should it be phrased differently?

I'm not sure. We never supported something like that so far, because the
expectation is that if it starts with a letter, it's a named mode. Thus
the named mode is PALe in your case, which doesn't match.

I'm not even sure what would be a good heuristic to support it, since
interpreting any e, E, or D as the last letter seems like a recipe for
disaster when some modes might legitimately end with e or d.

> It would have been nice to get a warning in the log if the parser fails
> to understand.
> 
> This very verbose version did work:
> video=Composite-1:720x576@...e,tv_mode=PAL-B

I think that's what we should be using in that case.

Maxime

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